Recently heterogeneous network deployments, where low power nodes of a pico cell are placed throughout a macro-cell, have gained significant interest from cellular network operators as a means to enhance system performance in terms of both coverage and capacity. A co-channel heterogeneous network deployment in which small power nodes use a same carrier frequency as an active macro cell is being studied at 3GPP. Under co-channel deployment, introduction of low power nodes into an active macro cell presents some challenges regarding reliability of control channels, in particular High Speed-Dedicated Physical Control Channel (HS-DPCCH) as well as the interference management between low power nodes (LPN) and high power nodes (HPN). Some issue may also arise regarding power measurements. Typically mobility in Wideband Code Division Multiple Access (WCDMA) is handled based at least in part on received power measurements of common pilot channel (CPICH). In a homogeneous network deployment where the transmission power of a base station such as a nodeB is same as a receiver's CPICH power measurement, both the transmission power and receiver power are proportional to pathloss of CPICH and thus reliable transmission of SI is not a serious concern. However, this may not be the case in a HetNet deployment.
For a soft handover (SHO) in a HetNet scenario, there may be an imbalanced uplink (UL)/downlink (DL) for the serving E-DCH cell. As a result of the link imbalance, the UL SI including UPH and data buffer status may not be received correctly by the serving E-DCH cell. More specifically, this may be related to the fact that power control (PC) for DPCCH is based on the best uplink of the radio link set (RLS) whereas the SI is only targeting the serving E-DCH cell which may have an uplink with lower link quality. Thus an SI message may fail to reach the serving E-DCH cell, at least in part due to the uplink imbalance in a SHO region. A solution is needed for a reliable SI transmission for multiplexed MAC-e/i PDU at least in a SHO region.
In general, SI reporting is either performed periodically based on a period defined by radio resource control (RRC) protocol as defined in 3GPP TS25.331 and/or triggered by an event of MAC layer as defined in 3GPP TS25.321. The triggers of SI reporting are also summarized in TS25.319 depending on whether the SI is sent along with the data. In short, UL SI may be transmitted to the serving E-DCH RLS as either a stand-alone MAC-e/i PDU or a part of a MAC-e/i PDU multiplexed with a MAC-d flow PDUs.
A User Equipment (UE) is allocated a Serving Grant (SG) which determines the rate at which scheduled data is transmitted. The SG is expressed in the terms of the power available for transmission. In a spread spectrum system, such as Wideband Code Division Multiple Access (WCDMA) and Universal Mobile Telecommunications System Frequency Division Duplexing (UMTS-FDD) used in HSUPA, the transmission power generally increases with the bit rate. Thus, a higher SG translates to a higher bit rate at which the UE can transmit data and so more scheduled data can be transmitted in a given time interval. The SG is used, along with other relevant parameters, to select an Enhanced Dedicated Transport Channel Transport Format Combination (E-TFC). The E-TFC is selected from a group of possible E-TFCs (defined in 3GPP TS 25.321 Version 11.2.0 Appendix B), with each E-TFC supporting a different transport block size. During the selection of an E-TFC to be transmitted, the SG is converted into a number of bits and used together with other relevant parameters to select the amount of useful data, expressed as a number of bits, which can be transmitted. Useful data is data which has a purpose and use in the communication system, and in HSUPA is the transmitted MAC-e or MACi PDU. The selected E-TFC is the one with the smallest transport block size which will allow the transmission of the useful data.
The following abbreviations are used in this application.
AG Absolute Grant
BS Base Station
CPICH Common Pilot Channel
CRC Cyclic redundancy check
DPCCH Dedicated Physical Control Channel
E-AGCH Enhanced Absolute Grant Channel
E-DCH Enhanced Data Channel
E-RGCH Enhanced Relative Grant Channel
E-TFC E-DCH Transport Format Combination
EUTRAN Enhanced UTRAN
HetNet Heterogeneous Network
HPN High Power Node
HPN BS High Power Node BS
HS-DPCCH High Speed-Dedicated Physical Control Channel
HSPA High Speed Packet Access
HUE HPN UE (UE served by HPN)
LPN Low Power Node BS
LTE Long Term Evolution
LUE LPN UE (UE served by LPN)
MAC Medium Access Control
MCS Modulation & Coding Scheme
OLPC Outer Loop Power Control
PC Power Control
RG Relative Grant
RLS Radio Link Set
RNC Radio Network Controller
SG Serving Grant
SHO Soft Handover
SI Scheduling Information
SIR Signal-to-Interference Ratio
SINR Signal to Interference Noise Ratio
TFC Transport Format Combination
TFCI Transport Format Combination Indicator
UE User Equipment
UMTS Universal Mobile Telecommunications System
UPH UE Power Headroom
UTRAN UMTS Radio Access Network